Printers, and in particular, serial printers, have taken many forms over the decades with the most common and widespread one being the typewriter. In recent years, the seemingly exponential increasing use of computer-based high speed information processing systems has placed a strong demand on serial printers in terms of speed, performance and reliability. A serial printer with control apparatus that is capable of meeting the ever more exacting contemporary requirements of speed, performance and reliability, is disclosed in copending application Ser. No. 682,877, filed on May 3, 1976 and assigned to the assignee of the present invention. As disclosed in this application, a record material is positively fed through the serial printer along a platen and past a printing station whereat the desired information is imparted to the record material, or paper. Since printer operation is obviously dependent on the availability of the paper, apparatus which can sense the absence (or presence) of record material in the printer and provide an indication of that condition to the printer (the printer in turn, if desired, causing printer shutdown and an indication to the printer operator that additional paper is required) would be desirable.
Prior art sensors which provided an indication whether printing paper was depleted and additional paper was to be added have been limited in application since the sensors utilized (i.e. photoelectric devices) were dependent, in part, on the paper width, the position of the paper on the platen and the thickness of the paper. These limitations have been overcome in the prior art by readjusting the sensors for each paper run in the printer, an obviously costly and time consuming procedure. Therefore, it would be desirable if apparatus could be provided which, inter alia, can sense the presence or absence of paper in a printer and which is essentially independent of paper width, paper thickness and the position of the paper on the platen.